The present invention relates to phosphors, and more particularly to improvements in red color - luminescent phosphors consisting essentially of rare earth oxysulfides activated with a trivalent europium, said phosphors being well adapted for use in a color television picture tube.
As is well known, a yttrium oxysulfide phosphor activated with europium is excellent as a red-color phosphor for use in a color television picture tube and hence finds a wide range of application in this field.
Japanese Pat. No. 537954 (Japanese Patent Publication No. Sho 43-21859) and U.S. Pat. No. 3,706,666 disclose such phosphors and their analogous materials, which contain oxychalcogenides of at least one member of a group consisting of yttrium and gadolinium, in addition to from 0.0002 to 0.2 mol of one member of a group consisting of europium, samarium, terbium and thulium,
In addition, it is known that the cathode-ray luminescent intensity is remarkably increased by adding up to 40 ppm of terbium or 100 ppm of praseodymium to the aforesaid phosphors, particularly, to yttrium and/or gadolinium oxysulfide activated with europium. Meanwhile, improvements in performance of phosphors for use in a color television are one of the important targets in this technology, which may provide economic advantages. Particularly, there has been a demand for improving yttrium oxysulfides activated with europium, which finds a wide range of application. As a result, it has been long desired to provide phosphors of this kind, which are lower in cost and higher in performance. Europium is a precious element which is not abundantly found among the rare earth elements, so that reduction in the amounts of europium without lowering the performance of phosphors would be of significant economic consequence.